According to German Patent No. 2,319,703, it is known to separate cobalt from nickel by a method which includes forming pentammine sulfate complexes of the two ions in solution. However, it has been found that soluble cobalt ammine sulfates can only be reduced while still in solution, under pressure, and with the aid of catalysts. Furthermore, the resulting cobalt powder is not fine particle size.
U.S. Pat. No. 4,093,450 to Doyle et al. describes a method for producing fine particle size cobalt metal powder by the hydrogen reduction of cobalt oxide obtained from a cobalt pentammine carbonate solution. The precipitate was formed by heating the solution to drive off ammonia and carbon dioxide to form a precipitate of cobalt oxide. This method requires a solution of approximately four grams per liter of cobalt to produce a sized metal powder having a particle size less than one micron. Note that the final resulting particle size is highly dependent on the concentration of cobalt employed in the aqueous solution.
The following patents are directed to the separation of cobalt from other cations, especially nickel. The resulting cobalt compounds are not disclosed as being sources for forming fine particle size cobalt.
U.S. Pat. No. 2,879,137 to Bare et al. discloses the treatment of an ammoniacal ammonium carbonate solution, obtained from leaching an ore and containing nickel wherein the cobalt present in the cobaltic state is treated with an alkali metal or alkaline earth metal hydroxide under controlled temperature conditions to precipitate the nickel free of cobalt.
U.S. Pat. No. 3,928,530 to Bakker et al. discloses a method for the separation of nickel and cobalt by forming pentammine chloride complexes and solution containing a high concentration of ammonium chloride, and precipitating cobalt pentammine chloride.
In German Patent No. 1,583,864, cobalt is recovered from scrap by digestion of the scrap in HCl and MgCl.sub.2 solution, followed by removal of iron and chromium impurities by precipitation at a moderately acid pH followed by extracting a cobalt chloride complex with a long chain tertiary ammine in an aromatic solvent.
U.S. Pat. No. 4,108,640 to Wallace discloses a method for recovering metallic cobalt from an aqueous ammoniacal solution wherein the solution is contacted with a water immiscible liquid ion exchange reagent dissolved in an inert organic diluent to selectively extract the other metal from the solution and produce an organic extract loaded with the other metals in an aqueous cobalt bearing raffinate substantially free of the other metals.